SEO
Search Engine Optimization - the set of practices for improving a website's organic visibility in search engine results pages without paying for placement. Encompasses on-page, off-page and technical optimisations.
SEM
Search Engine Marketing - umbrella term covering both organic SEO and paid search advertising (PPC). In common usage, SEM often refers exclusively to paid advertising on Google Ads and similar platforms.
SERP
Search Engine Results Page - the page returned by a search engine in response to a user query. Can contain organic results, paid ads, featured snippets, knowledge panels, images, videos and local packs.
CTR
Click-Through Rate - ratio of clicks to impressions expressed as a percentage: CTR = Clicks / Impressions × 100. Used both for organic results (monitored via Google Search Console) and for ads (PPC platforms).
CPA
Cost Per Acquisition - average cost to obtain a single conversion (sale, lead, app install): CPA = Spend / Conversions. Note: CPA measures any type of conversion, not just paying customers - unlike CAC (Customer Acquisition Cost) which is specific to acquiring new paying customers.
CAC
Customer Acquisition Cost - average cost to acquire a single new paying customer: CAC = Total Marketing + Sales Spend / New Customers in Period. Unlike CPA (which covers any type of conversion), CAC is specific to paying customers and typically includes all marketing, sales and onboarding costs.
ROAS
Return on Ad Spend - revenue generated per unit of advertising spend: ROAS = Campaign Revenue / Ad Spend. A ROAS of 4 means €4 of revenue for every €1 invested. Does not account for operating costs, unlike ROI which is a comprehensive profitability metric.
CPC
Cost Per Click - the amount an advertiser pays each time a user clicks on an ad. In PPC platforms, the effective CPC depends on the auction, ad quality (Quality Score) and the maximum bid.
CPM
Cost Per Mille - cost per one thousand ad impressions. Typical pricing model for brand awareness and display advertising campaigns: CPM = (Total Cost / Impressions) × 1,000.
CWV
Core Web Vitals - user experience metrics defined by Google. Includes LCP, INP and CLS. Confirmed Google ranking signals measuring page loading speed, input responsiveness and visual stability.
LCP
Largest Contentful Paint - time needed for the largest visually relevant content (hero image, H1 heading) to be rendered in the visible browser area. Google considers LCP < 2.5 s good.
INP
Interaction to Next Paint - overall latency of user interactions during the entire page visit (replaces FID from March 2024). Google considers INP < 200 ms good.
CLS
Cumulative Layout Shift - sum of unexpected layout shifts during page load. A CLS > 0.1 is considered needing improvement. Typically caused by images without declared dimensions or dynamically injected content.
KD
Keyword Difficulty - proprietary metric (Ahrefs, Semrush, Moz) estimating how difficult it is to organically rank for a keyword, primarily based on the backlink strength of pages already ranking in the top 10.
DA
Domain Authority - Moz metric (scale 1-100) estimating a whole domain's ability to rank in search engines. Useful proxy for competitive analysis; not a direct Google ranking signal.
PA
Page Authority - Moz metric (scale 1-100) estimating the ranking strength of a single page. Page-level analog of Domain Authority.
PPC
Pay Per Click - advertising model where the advertiser pays only when a user clicks on the ad. Google Ads is the main PPC platform. Synonymous with paid search in the search engine context.
ROI
Return on Investment - comprehensive profitability metric: ROI = (Net Profit - Investment) / Investment × 100. Includes all costs, unlike ROAS which only considers ad spend relative to campaign revenue.
UX
User Experience - the overall quality of a user's interaction with a website or digital product. A positive UX (intuitive navigation, speed, accessibility) reduces bounce rate and increases conversions, producing positive behavioural signals for SEO.
CVR
Conversion Rate - ratio of conversions to visitors (or sessions): CVR = Conversions / Sessions × 100. Measures the effectiveness of a page or campaign in converting traffic into desired actions.
LTV
Lifetime Value (also CLV - Customer Lifetime Value) - total expected value from a customer over the entire business relationship: LTV = Average Order Value × Purchase Frequency × Relationship Duration. The LTV/CAC ratio measures acquisition sustainability.
SSL/HTTPS
Secure Sockets Layer / HyperText Transfer Protocol Secure - encryption protocol protecting data transmission between browser and server. HTTPS is a minor but confirmed Google ranking signal. Technical prerequisite for user trust, especially on checkout and login pages.
CDN
Content Delivery Network - a geographically distributed network of servers delivering a site's static resources (images, CSS, JS) from the node closest to the user. Reduces latency and improves LCP and TTFB, with positive effects on CWV.
TTFB
Time to First Byte - time elapsed between the browser's HTTP request and receipt of the first response byte from the server. A TTFB < 0.8 s is considered good by Google. Depends on hosting, caching, server optimisation and CDN.
E-E-A-T
Experience, Expertise, Authoritativeness, Trustworthiness - the content quality evaluation framework used by Google Quality Raters. High-quality content demonstrates first-hand experience (Experience), subject-matter knowledge (Expertise), authority in the field (Authoritativeness) and trustworthiness to users (Trustworthiness). Particularly relevant for YMYL content.